1. Field of the Invention
The present invention relates to a caged roller assembly having a high load bearing capacity within a limited space and a planetary reduction gear unit using such caged roller assembly.
2. Description of the Prior Art
It is known that caged roller assemblies or caged roller assemblies are used in planetary reduction gear unit employed in various applications including, for example, construction machines. This type of caged roller assemblies has long been and is currently desired to have an increased load bearing capacity. While a full type roller assembly without a roller retainer is currently available as a bearing capable of exhibiting a maximum load bearing capacity within a limited space, it has been recognized that the full type roller assembly has a handling problem, specifically difficulty in assemblage and overhauling, and often involves a potential functional problem in that some of the rollers tend to skew during the use of the bearing. To alleviate these problems recognized in the art, various caged roller assemblies have been suggested.
For example, there exists a well known caged roller bearing which comprises a plurality of rollers and a circumferentially extending annular roller retainer having pockets spaced an equal distance from each other in a direction circumferentially of the roller retainer to accommodate the rollers, and the roller retainer has the pillars that extend from a radially inner side to a radially outer side of the roller retainer. Each pillar is formed in, for example, V-shape and provided with radially outer and inner roller stoppers to retain the roller in position. With this structure, since the pillar extending radially is disposed between the neighboring rollers, it is difficult to decrease a circumferential space between such rollers to thereby increase the number of rollers employed therein.
FIGS. 8A and 8B illustrate another prior art caged roller assembly designed to increase the number of rollers employed therein. The caged roller assembly shown therein comprises a circumferentially extending annular roller retainer 51 having opposite ends formed with annular collars 51b, and a plurality of rollers 52 rotatably accommodated within respective pockets 53 defined in the roller retainer 51 so as to be spaced an equal distance from each other in a direction circumferentially of the roller retainer 51 and as to leave a pillar 57 between the neighboring pockets 53. Where the number of the rollers 52 is increased, each of the pillars 57 has no way other than to be reduced in width, resulting in such a shape as shown in FIG. 8B.
Prior to the caged roller assembly of FIGS. 8A and 8B being mounted in, for example, a machine or a reduction gear unit, the prior art caged roller assembly is in such a condition that the rollers 52 is highly susceptible to separation or fall from the associated pockets in a direction radially inwardly of the roller retainer 51 although separation or fall of the rollers 52 in a direction radially outwardly of the roller retainer 51 is effectively refrained. Considering the ease to mount the caged roller assembly in a machine or reduction gear unit, means is necessitated to prevent the rollers 52 from inadvertently separating or falling out of the associated pockets 53 radially inwardly as well as radially outwardly by the time the caged roller assembly is ready to be mounted in the machine or reduction gear unit.
In view of the foregoing, the present invention has been devised to provide an improved caged roller assembly capable of exhibiting a high load bearing capacity even within a limited space substantially without some or all of the rollers being skewed during use thereof, and in which roller assembly prior to the caged roller assembly being mounted in a machine or reduction gear unit, separation or fall of some or all of the rollers out from the pockets in both directions radially inwardly and outwardly of the roller retainer is effectively prevented to facilitate a quick mounting or installation of the caged roller assembly in the machine or reduction gear unit.
A further important object of the present invention is to provide the improved caged roller assembly of the type referred to above, wherein means is provided to minimize depletion of a lubricant oil from a rolling surface to thereby prevent the roller retainer from being worn in frictional contact with the rollers.
The present invention has additional objects and features which would become apparent from the detailed description of preferred embodiments thereof that is herein set fort.
In order to accomplish these and other objects of the present invention, the present invention in accordance with one aspect thereof provides a caged roller assembly which includes a roller retainer including a large-diameter circumferential ring body having ends opposite to each other and a pair of annular flanks extending radially inwardly from the respective ends of the circumferential ring body, and a plurality of rollers rotatably carried by the roller retainer. The circumferential ring body has a plurality of circumferentially spaced pockets defined therein and the rollers are rotatably positioned within the respective pockets. Each of said rollers has opposite end faces each formed with an axially inwardly extending bearing recess defined therein. Bearing bosses are formed in each of the annular flanks in a circular row one for each of the pockets, the circular row of the bearing bosses in each annular flank being aligned with a pitch circle that is defined by respective axes of rotation of the rollers. The bearing bosses in the annular flanks are rotatably engaged in the bearing recesses on the opposite end faces of the associated rollers, said circumferential ring body having a diameter greater than the pitch circle of the rollers.
According to the structure described above, prior to the caged roller assembly of the present invention being mounted in a machine or reduction gear unit, not only is any possible separation of the rollers in a direction radially outwardly from the roller retainer prevented by opposite side edges of the pockets, but also any possible separation of the rollers in a direction radially inwardly from the roller retainer is prevented by the bearing bosses rotatably engaged in the bearing recesses at the opposite end faces of the rollers. Since each of the pillars of the roller retainer situated between the neighboring pockets is provided only on a radially outer side of the roller retainer, as compared with the roller retainer having the pillars that extend from a radially inner side to a radially outer side of the roller retainer such as in the prior art caged roller assembly, the roller retainer used in the present invention can have a simplified shape and be easy to manufacture, allowing to expand the limit to which each pillar situated between the neighboring pockets can be reduced in width. Accordingly, the number of the rollers that can be employed within a predetermined space available in the caged roller assembly can advantageously be increased to thereby increase the load bearing capacity of the resultant caged roller assembly. The bearing recesses defined in the opposite end faces of each of the rollers, in which the corresponding bearing bosses rigid or fast with the annular flanks engage also serve as oil sumps and, therefore, the frictional wear of respective portions of the annular flanks that are held in sliding contact with the end faces of the rollers can advantageously be minimized.
The manner in which the rollers are guided by the roller retainer can be classified into two types depending on the dimensional relationship. Where a gap between each roller and the adjacent side face of each pillar between the neighboring pockets is small relative to the size of a radial gap (play) between the bearing recess in each end face of the rollers and the associated bearing boss of the roller retainer that is engaged in such bearing recess, each roller can be guided by the pillars on respective sides of such roller. On the other hand, where the gap between each roller and the adjacent side face of each pillar between the neighboring pockets is conversely large, each roller can be guided by a portion where the bearing recess in each end face of the rollers and the associated bearing boss of the roller retainer are engaged with each other. In either cases, the rollers are guided by the roller retainer and, therefore, as compared with the full type roller assembly, any possible occurrence of skewing of some or all of the rollers can be advantageously minimized or substantially eliminated.
According to the present invention, depletion of an oil film on a rolling surface can be minimized in the following manner. In the well known prior art caged roller assembly discussed above, since the rollers are retained in position by the radially outer and inner roller stoppers formed on respective pillars of the roller retainer, it has often been observed that the oil film on the rolling surfaces of the rollers tends to be depleted in sliding contact with the roller stoppers. In contrast thereto, the present invention makes no use of such roller stoppers and, instead thereof, utilizes the side faces of the pillars to support the rollers and/or the bearing recesses in the opposite end faces of the rollers to retain the roller and, therefore, any possible depletion of the oil film on the rolling surfaces can be minimized.
The present invention in accordance with another aspect thereof provides the caged roller assembly wherein the circumferential ring body and the annular flanks both used in the caged roller assembly according to the foregoing aspect of the present invention are reversed in position relative to each other. More specifically, the caged roller assembly according to this aspect of the present invention includes a roller retainer including a large-diameter circumferential ring body having ends opposite to each other and a pair of annular flanks extending radially outwardly from the respective ends of the circumferential ring body, and a plurality of rollers rotatably carried by the roller retainer. The circumferential ring body has a plurality of circumferentially spaced pockets defined therein and the rollers are rotatably positioned within the respective pockets. Each of said rollers has opposite end faces each formed with an axially inwardly extending bearing recess defined therein. Bearing bosses are formed in each of the annular flanks in a circular row one for each of the pockets, the circular row of the bearing bosses in each annular flank being aligned with a pitch circle that is defined by respective axes of rotation of the rollers. The bearing bosses in the annular flanks are rotatably engaged in the bearing recesses on the opposite end faces of the associated rollers, said circumferential ring body having a diameter smaller than the pitch circle of the rollers.
Even in this alternative design, prior to the caged roller assembly of the present invention being mounted in a machine or reduction gear unit, not only is any possible separation of the rollers in a direction radially inwardly from the roller retainer prevented by opposite side edges of the pockets, but also any possible separation of the rollers in a direction radially outwardly from the roller retainer is prevented by the bearing bosses rotatably engaged in the bearing recesses at the opposite end faces of the rollers. Since each of the pillars of the roller retainer situated between the neighboring pockets is provided only on a radially inner side of the roller retainer, as compared with the roller retainer having the pillars that extend from a radially inner side to a radially outer side of the roller retainer such as in the prior art caged roller assembly, the roller retainer used in the present invention can have a simplified shape and be easy to manufacture, allowing to expand the limit to which each pillar situated between the neighboring pockets can be reduced in width. Accordingly, the number of the rollers that can be employed within a predetermined space available in the caged roller assembly can advantageously be increased to thereby increase the load bearing capacity of the resultant caged roller assembly.
Also, as is the case with the caged roller assembly according to the first mentioned aspect of the present invention, not only can any possible skewing of the rollers be minimized or substantially eliminated, but also the bearing recesses serve as oil sumps. Therefore, the frictional wear of respective portions of the annular flanks that are held in sliding contact with the end faces of the rollers can advantageously be minimized, and any possible depletion of the oil film on the rolling surfaces can also be prevented.
In the practice of the present invention, while each of the pockets is defined by opposite end walls and opposite side walls, leaving a pillar that is situated between the neighboring pockets while extending between the annular flanks, each of the opposite side walls of the respective pocket may be inwardly depressed at a generally intermediate portion thereof to define roller guides on respective sides of the inwardly depressed region.
According to this preferred design, while the roller guides on respective sides of the inwardly depressed region in each of the pillars provides a function of guiding the associated roller, the inwardly depressed regions ensures a smooth flow of a lubricant oil. If each roller is guided by the opposite side walls of the adjacent pocket over the entire length thereof, a smooth flow of the lubricant oil will be hampered, but the presence of the inwardly depressed regions is effective to eliminate any obstacle to the smooth flow of the lubricant oil. Accordingly, any possible loss of torque during rotation can advantageously be eliminated.
In a preferred embodiment of the present invention, while each of the pockets is defined by opposite end walls and opposite side walls, leaving a pillar that is situated between the neighboring pockets while extending between the annular flanks, and the opposite side walls of the respective pocket serve as roller guides, the pillar may have a transverse sectional shape wherein a peripheral lip region of an outer peripheral surface of the pillars is positioned radially inwardly of the outer peripheral surface of the circumferential ring body and adjacent the pitch circle.
When the peripheral lip region of the outer peripheral surface of the pillar is positioned radially inwardly of the outer peripheral surface of the circumferential ring body and adjacent the pitch circle, scraping of the lubricant oil by an edge of the peripheral lip region around each pocket can be lessened to thereby suppress a loss of torque which would otherwise occur during rotation as a result of lack of the lubricant oil.
In another preferred embodiment of the present invention, each of the bearing bosses may protrude outwardly from the respective annular flank a distance smaller than a depth of the respective bearing recess on the end face of each roller.
When the height of each bearing bosses is so defined, the tip or free end of each bearing bosses does not contact the bottom of the associated bearing recess and, instead, the end faces of the roller may slidingly contact surface portions of the annular flanks around the bearing bosses. For this reason, no local contact of the tips of the bearing bosses will occur, lessening frictional wear.
Preferably, the roller retainer is made of a synthetic resin. The use of a synthetic resin as a material for the roller retainer allows the roller retainer having the bearing bosses to be easily and efficiently manufactured.
Also preferably, the caged roller assembly may be used in a planetary reduction gear unit including a planetary gear and a crankshaft, in which case the caged roller assembly is disposed between the planetary gear and the crankshaft.
The present invention also provides a planetary reduction gear unit which utilizes the caged roller assembly of the structure discussed hereinabove. More specifically, the planetary reduction gear unit to which the present invention is applied includes an internally or externally geared sun gear, a carrier provided coaxially of the sun gear, at least one crankshaft rotatably supported by the carrier and having a plurality of eccentric cam portions, and a planetary gear mounted on each of the eccentric cam portions of the crankshaft through the associated caged roller assembly and drivingly meshed with the sun gear. The caged roller assembly of the present invention operatively intervenes between the planetary gear and the respective eccentric cam portion of the crankshaft.
The planetary reduction gear unit in which the planetary gears are mounted on the crankshaft must be of a design in which the caged roller assembly intervening between each of the planetary gears and the crankshaft should not interfere an inner diameter of the adjacent planetary gear. According to the present invention, this interference is avoided owing to the annular collars or flanks of the roller retainer. Also, in the planetary reduction gear unit of this kind, support of the planetary gears requires a relatively large load and a support sections tends to be a limited space. However, the use of the caged roller assembly in which the bearing bosses formed with the annular collars or flanks are engaged in the corresponding bearing recesses formed in the opposite end faces of the rollers permits the number of the rollers used to be increased within the margin of the limited space and, therefore, a relative large load bearing capacity can be obtained. Consequently, the planetary gear unit can be made compact in size, and installation of the caged roller assembly in the unit is facilitated.